The threat of bioterrorism (BT) and biological warfare presents challenges for the clinical setting that are best met with rapid and sensitive technologies to detect BT agents. Peripheral blood samples could contribute to early and specific clinical and epidemiological management of a biological attack if detection could take place when the concentration of the infecting organism is still very low. The worried well and recently infected patients would benefit, both psychologically and physically, from early pharmacological intervention.
Infection with Bacillus anthracis or Yersinia pestis often present initially as a nonspecific febrile or flu-like illness. The mediastinitis associated with inhalational anthrax ultimately results in bacilli entering the blood once the efferent lymphatics become laden with organisms. When bacteremia (the presence of bacteria in the blood) and sepsis (the invasion of bodily tissue by pathogenic bacteria) have initiated, the number of bacilli may increase quickly, doubling every 48 minutes, most often resulting in death of the patient.
It has been reported that microbiological studies on patient blood samples are useful for diagnosing pneumonic plague. The potential for Yersinia pestis bacilli to be present in peripheral circulating blood suggests that a PCR assay would make a useful diagnostic tool. Testing for pneumonic plague or inhalational anthrax would be effective when healthy patients present with “flu-like” symptoms (malaise, fever, cough, chest pain and shortness of breath) that may accompany other nonspecific symptoms. However, in order to maximize the probability of successful treatment, detection of the infecting organism must take place early in the disease process, when the concentration of circulating bacteria is very low.
Extraction of pathogen DNA from whole blood typically requires between 200 μl to 500 μl of whole peripheral blood patient sample for each preparation event. Detection of early bacteremia is improved by using an entire 6 to 10 ml tube of patient blood for a single sample preparation event. Prior art literature describes a single tube blood culture system exploiting the selective lysis of blood elements, followed by centrifugation to pellet bacteria for plating on solid media. The technique has been examined thoroughly in conjunction with microbiological testing. Previous methods based on lyses of blood cells followed by centrifugation have not proven to be useful for nucleic acid or biosensor based detection protocols.
Accordingly, what is needed in the art is: 1) a method of destroying and making soluble the spectrum of blood element components (erythrocytes, leukocytes, nuclear membranes, fibrin, and host nucleic acid) without damaging analyte particles (bacteria, virus, fungi, toxin, metabolic markers, disease state markers, or chemical agents) in order to expose and rapidly concentrate (via centrifugation, filtration, or capture) the analyte particles from large volumes of blood, 2) processing to minimize inhibition and/or removal of the host DNA and the matrix associated biomass present in the large volume blood sample using a single step enzyme detergent cocktail that is amenable to automation and portable systems, and 3) an analyte particle concentration method that can be coupled to existing manual or automated processes for nucleic acid extraction, biosensor testing, or liquid chromatography separation and mass spectrometry analysis. It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.
Fibrin is an insoluble protein precipitated from blood that forms a network of fibers. In vivo, this process is central to blood clotting. Fibrin is created by the proteolytic cleavage of terminal peptides in fibrinogen. In the laboratory analysis of blood, an aggregate (pellet) of fibrin combined with other blood elements sediments at the bottom of a tube when blood is centrifuged. Within the fibrin aggregate, pathogens are trapped. The analysis of these pathogens is highly desirable. However, like coins embedded in a slab of concrete, the captured pathogens are substantially hidden from analysis, trapped in the fibrin aggregate. For individuals potentially exposed to dangerous pathogens, time is of the essence and rapid identification of the captured pathogens is paramount. Rapid identification of nucleic acid, proteins, or other molecules associated with bacteria, virus, fungi, toxin, metabolic markers, disease state markers, or chemical agents is important for individual clinical management as well as forensic and epidemiological investigation.
Plasmin is a substance in blood capable of converting fibrin to fibrinogen monomers. Plasminogen is a precursor of plasmin in the blood. Streptokinase is an enzyme that activates plasminogen to form plasmin. The combination of plasminogen and streptokinase in the presence of the fibrin aggregate containing blood elements and bacteria (formally present in peripheral circulation) allows the conversion of the fibrin aggregate to a liquid state. Plasminogen activators are naturally occurring enzymes found in most all vertebrate species. These enzymes in any combination can also be used to derive beneficial blood matrix disassembly where the downstream application require clots or blood element aggregates to be dissolved in order to facilitate sample flow and analyte interrogation.
Aurintricarboxylic acid (ATA) is a polymeric anion that has been demonstrated in the literature to be a potent ribonuclease inhibitor. The compound has been described previously as an additive to sample lysis buffers where the objective is to extract RNA species from tissue samples. The nucleic acid extract derived from such procedures has been shown to be suitable for hybridization and gel electrophoresis analysis. However, ATA is a potent inhibitor of reverse transcriptase, which is essential for the polymerase chain reaction (PCR) detection of RNA species. Published procedures to remove ATA from nucleic acid containing compositions have revolved around chromatographic procedures that eliminate or remove only a portion of the ATA.
The use of ATA in a proteinase K lysis buffer is potentially superior to 1) chaotrophic salts (since they tend to reduce the efficiency of proteinase K driven protein hydrolysis as evidenced by PCR results); 2) protein based ribonuclease inhibitors (since these inhibitors would be broken down by proteinase K); and 3) EDTA (which only indirectly inhibits nucleases via chelation of the divalent cations used by those nucleases). In fact, divalent cations must be added to RNA preparations where enzymatic DNA hydrolysis is conducted. What has not been demonstrated in prior art is a method where, once added, the complete downstream removal of ATA from nucleic acid extracts can be achieved to the point that downstream reverse transcriptase PCR (RT-PCR) will function. Also not previously described is a way to utilize ATA in a lyses buffer to treat a large volume (1 to 10 ml) of whole blood sample and after several reagents addition steps move directly to RNA array hybridization using the entire blood sample for one analysis event hence bypassing RNA extraction and amplification.
Also not previously described is a way to selectively allow non-diagnostic RNA species residing outside the nucleus of leukocytes to be degraded by endogenous and or exogenous nucleases while diagnostic RNA which mostly resides inside the nucleus (RNA that for instance indicates up or down regulation of genes) is preserved enough for array or amplification based detection. Typically, chemistries that do not provide abundant intact ribosomal RNA are not further examined because end users skilled in the art use such non diagnostic RNA species to judge overall RNA integrity. Based on biochemical and phenotypical differences between phospholipid membranes found in various blood elements and the combined biochemical activity characteristics of the reagent cocktail, RNA species such as globin and ribosomal RNA are destroyed but the diagnostic mRNA which is used to detect presence or absence of various disease and or pathological processes is preserved enough for identification. Also, by allowing for the bulk of non-diagnostic RNA to be destroyed, there is less inhibition of PCR (polymerase chain reaction) contributed by the nucleic acid extract.
ATA also serves an important function in the protection of bacterial DNA when that bacteria is present in a blood sample processed with reagents containing high levels (≧100 U/ml) of DNase I as is used in various embodiments contained within U.S. application Ser. No. 10/604,779. In order to achieve RNA detection capabilities that are superior to what can be achieved with technology descried in U.S. application Ser. No. 10/604,779, and to do so without additional steps or requirements, the present invention is utilized in combination with blood sample treatment technology described in U.S. application Ser. No. 10/604,779 and prior art nucleic acid extraction methods that utilize chaotrophic salts such as guanidine thiocyanate in the presence of capture matrices such as silica or methods that utilize precipitation methods to concentrate nucleic acids out of crude samples.